Yes, SECULAR is a Scrabble word!

Letter values in Scrabble US: S 1, E 1, C 3, U 1, L 1, A 1, R 1.

Is it a valid word?

SECULAR is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

of or relating to the doctrine that rejects religion and religious considerations
characteristic of or devoted to the temporal world as opposed to the spiritual world
not concerned with or devoted to religion
of or relating to clergy not bound by monastic vows
characteristic of those who are not members of the clergy